Capacitive sensors used for proximity sensing are generally known; however, such sensors do not adequately control stray capacitance and consequently do not perform with an adequate range and sensitivity for many applications. To overcome these limitations, the sensors are often mounted at substantial distances from the machinery, thus reducing their effectiveness.
The purpose of the present invention is to provide a proximity sensor for a robot arm that will sense intruding objects so that the robot controller can prevent the robot from colliding with objects in space, particularly a human being. This sensor must be able to function reliably in the extreme environment of outer space and operates so as not to disturb or be disturbed by neighboring instruments. It must be simple, compact and incidental to the robot design and be able to detect objects at ranges in excess of 12 inches so that the robot has sufficient time to react. In the past a capacitive sensor typically was mounted in a stand-off relationship from the grounded robot arm a considerable distance, typically 1 in. from the outer surface of the arm. This tends not only to disfigure the robot arm, but causes it to be bulkier than necessary. It also makes cross talk between the sensor elements more pronounced and tends to impede the flow of heat from the robot arm to outer space.
Although the driven shield technique is also known in conjunction with capacitive sensors to prevent stray capacitance in lead wires and to increase input impedance, it has also been utilized in connection with tactile sensors where pressure is exerted against one or both plates of a capacitor.